WASHINGTON – The U.S. Coast Guard has ordered large ferry operators to step up security on more than 300 passenger ships across the country, including Maine, in the wake of the terrorist attacks in London.

The heightened security could cause delays for passengers, who will see increased screening of their vehicles, more identification checks and more law enforcement officers patrolling the ferries.

Coast Guard vessels will escort ferries, and recreational boaters should be aware of security zones and restricted waters around marine transportation routes, said spokesman Lt. Commander Jeff Carter.

“We have no specific intelligence indicating a direct threat to ferries,” said Carter. “However, it is prudent to increase security on this vital transportation link that carries more than 135 million people each year.”

Passengers have been advised to arrive 30 minutes before departure on some ferry systems – twice the normal time – to allow for the additional screening.

The largest number of passenger ferries is concentrated on the Northeast and Pacific Northwest coasts.

Washington state operates the largest system in the United States, carrying more than 25 million passengers each year. Other large ferry operators are located in New York, Massachusetts, Connecticut, Delaware, Maine, Virginia, North Carolina, Louisiana, Michigan, Texas and Alaska.

Adding personnel or extending work hours for the increased security are the biggest expenses for the ferry operators, many of which are state- or city-owned, said Beth Gedney, safety director for the Passenger Vessel Association. She said another major concern is the possible loss of customers because of the boarding delays.